The visual pigments of man are formed by the interaction of a polyene chromophore, 11-cis-retinal sub 1, and a protein moiety termed opsin. All other known animal visual pigments have the same general structure and have either 11-cis-retinal sub 1 or 11-cis-3- dehydroretinal sub 2 as their chromophore. The absorption and activation spectra of visual pigments show a wide range of lambda max values, and abnormal human vision has been correlated with abnormalities or absence of retinal visual pigments. Visual pigments formed with but a single chromophore (e.g., 11-cis-retinal sub 1) may vary greatly in spectral sensitivity, and it is generally accepted that the opsin determines the lambda max of the visual pigment. Although there is disagreement about the exact nature of the linkage of the retinal chromophore in the native visual pigment, it appears that the fine structure of the opsin chromophore binding site defines the spectral characteristics of the visual pigment. This infers that different visual pigment opsins vary in primary structure. We propose to define and compare the primary structure of visual pigment proteins from different species, which display the same or different lambda max, in order that the regions of sequence conservation and sequence variation may be identified.